This invention relates to a remote viewing method and apparatus for use on fork lift trucks. This invention has particular application to those fork lift trucks where the forks can be raised above the head of the operator causing the operator difficulty in visually aligning the forks to a load or a load on the fork to an opening in a storage rack.
In many materials handling vehicles, such as a rider-reach truck or a three- or four-wheel counterbalanced truck, a pair of movable, load carrying forks are mounted on a carriage for vertical movement on the mast of the truck. A camera has sometimes been mounted near the heel of the forks to view the scene in front of the forks, and to display that scene on a monitor mounted in view of the operator. Such an arrangement is helpful, provided the camera is properly positioned so that its view is properly aligned with the forks; however, the view of a camera in this location will be blocked when a pallet is placed on the forks. With a load on the forks, the best position for the camera is below the bottom of the load for use in operator viewing under-clearance or viewing alignment with a target below the load; however, in this position, the camera is subject to damage when the forks are lowered near the floor on which the truck is operating. If the camera is fixed positioned to be clear of the floor when the forks are fully lowered, then its view will be too high to be effective for viewing below the forks and load.
The operator view problem is exacerbated on double reach trucks, that is, trucks with scissors mechanisms that permit the forks to be doubly extended, and thus pick up and deposit loads twice the storage depth distance of a single pallet. The operator's view of the double deep load position in the rack is not visible from this position.
Some lift trucks provide a fork tilt indicator; however, these indicators measure fork tilt relative to the truck's mast, not relative to a horizontal plane. Further, monitoring fork tilt either by sensing the vertical component of the fork or at the heel of the fork will not take into consideration the deflection of the fork away from the mast due to the weight of a load.